Manufacture of colloidal gold.



UN TED STATES CARL PAAL, OF ERLANGEN, GERMANY, ASSIGDIOR TO KALLE AND COM- PATENT OFFICE;

PANY, OF BIEBRICH, GERMANY, A FIRM.

MANUFACTURE OF COLLOIDAL GOLD.

SPECIFICATION forming part of Letters Patent No. 701,605, dated June 3, 1902.

' Application filed February 5, 1901. Serial No. 46,119. (No specimens.)

1o caustic alkalies. On dialyzin g the products of.

this decomposition, as Well as the albumoses in aqueous alkaline solution stable alkali salts of these albumin derivatives are obtained. I have now succeeded in preparing from gold salts by means of these alkali salts a new form of colloidal gold showing distinct properties.

I describe my new process by giving the following example; but I do not limit myself to the quantities and proportions given therein.

Ten parts, by weight, of an alkali salt of the decomposition products of albumins are dis solved in one hundred and fifty parts of water, adding forty .parts of caustic-soda lye of 2 5 twenty per cent. NaOH. Into the so obtained clear liquid I pour at a temperature of 70 to 80 centigrade a concentrated aqueous solution of fifteen parts chlorid of gold. I then heat this mixture on the water-bath until the 0 color of the liquid, which is yellow at the be-.

ginning, but soon turns bluish violet on heating, has changed into a bright red. The so obtained liquid is cooled and then dialyzed against water in order to remove as much of the inorganic substances (caustic soda, so-

dium chlorid) as possible. The dialyzed liquid is then heated to centigrade and completely precipitated by addition of acetic acid of thirty per cent. The precipitate is fil- 4o tered, washed, suspended in water, and redisparatus. In this manner I obtain a colloidal gold of over seventy per cent. pure gold consistin g of bright scales, showing a bronzy luster, and being Very easily soluble in water with an intensely-red coloration. The metal is precipitated from its aqueous solution by addition of dilute acids. The so-obtained heavy precipitate is insoluble in water, but it is quite easily dissolved again by very dilute aqueous alkali solutionscaustic potash, caustic soda, ammonia, and even sodium carbonate. By this property the colloidal gold obtained by my process is distinctly different from colloidal goldotherwise prepared,which is also precipitated from its'aqueous solutions by acids, but which completely loses by this treatment its solubility, also in dilute alkalies.

What I claim is 1. The new process of preparing colloidal gold by adding to an aqueous solution of the alkali salts of the decomposition products of albumins (formed by the action of warm dilute alkalies on albumins) caustic-soda lye and as much chlorid of gold as slightly exceeds the quantity corresponding to the alkali present, heating this mixture until its coloration has changed into a bright red, dialyzing it against water, precipitating it with a dilute acid, dissolving the precipitate in dilute caustic-soda lye, dialyzing the solution again, and evaporating it.

2. As a new product the colloidal gold,containing over sixty per cent. pure metal, consisting of bright scales showing a bronzy luster, being Very easily and completely soluble in water and distinguished by its property to retain its solubility in dilute aqueous alkalies even after having been precipitated from its aqueous solutions by means of acids.

In testimony whereof I have signed my name to this specification in the presence of two subscribing witnesses.

, CARL PAAL.

Witnesses:

RICHARD GUENTHER, IGNAS ROSENBERG. 

